Processes for forming an aldehyde by the reaction of an olefin with carbon monoxide and hydrogen in the presence of a solubilized solution of a Group VIII metal-trihydrocarbyl ligand complex catalyst are well known in the art.
In more recent developments the preferred Group VIII metal has been rhodium, while the preferred trihydrocarbyl ligand has been triarylphosphine such as triphenylphosphine.
For instance, U.S. Pat. No. 3,527,809, the entire disclosure of which is incorporated herein, discloses a hydroformylation process whereby alpha-olefins are hydroformylated with carbon monoxide and hydrogen to produce aldehydes in high yields at low temperatures and pressures, where the normal to iso-(or branched-chain) aldehyde isomer ratio of the product aldehydes is high. This process employs certain rhodium complex catalysts and operates under defined reaction conditions to accomplish the olefin hydroformylation and since this process operates at significantly low pressures, substantial advantages were realized including lower initial capital investment and lower operating costs. Further, the more desirable straight chain aldehyde isomer can be produced in high yields.
The hydroformylation process set forth in said U.S. Pat. No. 3,527,809 noted above includes the following essential reaction conditions:
(1) A rhodium complex catalyst which is a complex combination of rhodium with carbon monoxide and a triorganophosphorus ligand. The term "complex" means a coordination compound formed by the union of one or more electronically rich molecules or atoms capable of independent existence with one or more electronically poor molecules or atoms, each of which is also capable of independent existence. Triorganophosphorus ligands whose phosphorus atom has one available or unshared pair of electrons are capable of forming a coordinate bond with rhodium.
(2) An alpha-olefin feed of alpha-olefinic compounds characterized by a terminal ethylenic carbon-to-carbon bond such as a vinyl group CH.sub.2 .dbd.CH--. They may be straight chain or branched chain and may contain groups or substituents which do not essentially interfere with the hydroformylation reaction, and they may also contain more than one ethylenic bond. Propylene is an example of a preferred alpha-olefin.
(3) A triorganophosphorus ligand such as a triarylphosphine. Desirably each organo moiety in the ligand does not exceed 18 carbon atoms. The triarylphosphines are the preferred ligands, an example of which is triphenylphosphine.
(4) A concentration of the triorganophosphorus ligand in the reaction mixture which is sufficient to provide at least two, and preferably at least 5, moles of free ligand per mole of rhodium metal, over and above the ligand complexed with or tied to the rhodium atom.
(5) A temperature of from about 50.degree. to about 145.degree. C., preferably from about 60.degree. to about 125.degree. C.
(6) A total hydrogen and carbon monoxide pressure which is less than 450 pounds per square inch absolute (psia) preferably less than 350 psia.
(7) A maximum partial pressure exerted by carbon monoxide no greater than about 75 percent based on the total pressure of carbon monoxide and hydrogen, preferably less than 50 percent of this total gas pressure.
It is also known that, under hydroformylation conditions, some of the product aldehydes may condense to form by-product, high boiling aldehyde condensation products such as aldehyde dimers or trimers. Commonly-assigned U.S. Pat. No. 1,148,830, the entire disclosure of which is incorporated herein by reference thereto, discloses the use of these high boiling liquid aldehyde condensation products as a reaction solvent for the catalyst. In this process, solvent removal from the catalyst, which may cause catalyst losses, is unnecessary and, in fact, a liquid recycle containing the solvent high boiling aldehyde condensation products and catalyst is fed to the reaction zone from a product recovery zone. More specifically, as pointed out in said U.S. Pat. No. 4,148,830, some of the aldehyde product is involved in various reactions as depicted below using n-butyraldehyde as an illustration: ##STR1##
The names in parentheses in the afore-illustrated equations, aldol I, substituted acrolein II, trimer III, trimer IV, dimer V, tetramer VI, and tetramer VII, are for convenience only. Aldol I is formed by an aldol condensation; trimer III and tetramer VII are formed via Tischenko reactions; trimer IV by a transesterification reaction; dimer V and tetramer VI by a dismutation reaction. Principal condensation products are trimer III, trimer IV, and tetramer VII, with lesser amounts of the other products being present. Such condensation products, therefore, contain substantial quantities of hydroxylic compounds as witnessed, for example, by trimers III and IV and tetramer VII.
Similar condensation products are produced by self-condensation of iso-butyraldehyde and a further range of compounds is formed by condensation of one molecule of normal butyraldehyde with one molecule of iso-butyraldehyde. Since a molecule of normal butyaldehyde can adolize by reaction with a molecule of iso-butyraldehyde in two different ways to form two different aldols VIII and IX, a total of four possible aldols can be produced by condensation reactions of a normal/iso mixture of butyraldehydes. ##STR2##
Aldol I can undergo further condensation with isobutyraldehyde to form a trimer isomeric with trimer III and aldols VIII and IX and the corresponding aldol X produced by self-condensation of two molecules of isobutyraldehyde can undergo further reactions with either normal or isobutyraldehyde to form corresponding isomeric trimers. These trimers can react further analogously to trimer III so that a complex mixture of condensation products is formed.
In addition commonly-assigned copending U.S. application Ser. No. 776,934, filed Mar. 11, 1977, now U.S. Pat. No. 4,247,486, the entire disclosure of which is incorporated herein by reference thereto, discloses a liquid phase hydroformylation reaction using a rhodium complex catalyst, wherein the aldehyde reaction products and some of their higher boiling condensation products are removed in vapor form from the catalyst containing liquid body (or solution) at the reaction temperature and pressure. The aldehyde reaction products and the condensation products are condensed out of the off gas from the reaction vessel in a product recovery zone and the unreacted starting materials (e.g., carbon monoxide, hydrogen and/or alpha-olefin) in the vapor phase from the product recovery zone are recycled to the reaction zone. Furthermore, by recycling gas from the product recovery zone coupled with make-up starting materials to the reaction zone in sufficient amounts, it is possible, using a C.sub.2 to C.sub.5 olefin as the alpha-olefin starting material, to achieve a mass balance in the liquid body in the reactor and thereby remove from the reaction zone at a rate at least as great as their rate of formation essentially all the higher boiling condensation products resulting from self-condensation of the aldehyde product.
More specifically, according to said Ser. No. 776,934, a process for the production of an aldehyde containing from 3 to 6 carbon atoms is disclosed which comprises passing an alpha-olefin containing from 2 to 5 carbon atoms together with hydrogen and carbon monoxide at a prescribed temperature and pressure through a reaction zone containing the rhodium complex catalyst dissolved in a liquid body, continuously removing a vapor phase from the reaction zone, passing the vapor phase to a product separation zone, separating a liquid aldehyde containing product in the product separation zone by condensation from the gaseous unreacted starting materials, and recycling the gaseous unreacted starting materials from the product separation zone to the reaction zone.
It is also known in the prior art that even in the absence of intrinsic poisons there may be deactivation of rhodium hydroformylation catalysts under hydroformylation conditions. Copending, commonly-assigned U.S. patent application Ser. No. 762,336 filed Jan. 25, 1977, abandoned in favor of continuation U.S. application Ser. No. 151,293, the entire disclosure of which is incorporated herein by reference thereto, indicates that the deactivation of rhodium hydroformylation catalysts under hydroformylation conditions in the substantial absence of extrinsic poisons is due to the combination of the effects of temperature, phosphine ligand:rhodium mole ratio, and the partial pressures of hydrogen and carbon monoxide and is termed an intrinsic deactivation. It is further disclosed therein that this intrinsic deactivation can be reduced or substantially prevented by establishing and controlling and correlating the hydroformylation reaction conditions to a low temperature, low carbon monoxide partial pressure and high free triarylphosphine ligand:catalytically-active rhodium mole ratio. More specifically, this application discloses a rhodium-catalyzed hydroformylation process for producing aldehydes from alpha-olefins including the steps of reacting the olefin with hydrogen and carbon monoxide in the presence of a rhodium complex catalyst consisting essentially of rhodium complexed with carbon monoxide and a triarylphosphine, under certain defined reaction conditions, as follows:
(1) a temperature of from about 90.degree. to about 130.degree. C.;
(2) a total gas pressure of hydrogen, carbon monoxide and alpha-olefin of less than about 400 psia;
(3) a carbon monoxide partial pressure of less than about 55 psia;
(4) a hydrogen partial pressure of less than about 200 psia;
(5) at least about 100 moles of free triarylphosphine ligand for each mole of catalytically active rhodium metal present in the rhodium complex catalyst; and controlling and correlating the partial pressure of carbon monoxide, the temperature and the free triarylphosphine:catalytically active rhodium mole ratio to limit the rhodium complex catalyst deactivation to a maximum determined percent loss in activity per day, based on the initial activity of the fresh catalyst. By "catalytically active rhodium" is meant the rhodium metal in the rhodium complex catalyst which has not been deactivated. The amount of rhodium in the reaction zone which is catalytically active may be determined at any given time during the reaction by comparing the conversion rate to product based on such catalyst to the conversion rate obtained using fresh catalyst.
The manner in which the carbon monoxide partial pressure, temperature and free triarylphosphine:catalytically active rhodium mole ratio should be controlled and correlated to thus limit the deactivation of the catalyst is illustrated as follows.
As an example, for the triarylphosphine ligand triphenylphosphine, the specific relationship between these three parameters and catalyst stability is defined by the formula: ##EQU1## where
F=stability factor
e=Naperian log base (i.e., 2.718281828)
y=K.sub.1 +K.sub.2 T+K.sub.3 P+K.sub.4 (L/Rh)
T=reaction temperature (.degree.C.)
P=partial pressure of CO (psia)
L/Rh=free triarylphosphine:catalytically active rhodium mole ratio
K.sub.1 =-8.1126
K.sub.2 =0.07919
K.sub.3 =0.0278
K.sub.4 =-0.01155
As pointed out in said Ser. No. 762,336, an olefin response factor must be employed to obtain the stability factor under actual hydroformylation conditions. Olefins generally enhance the stability of the catalyst and their effect on catalyst stability is more fully explained in said application. The above relationship is substantially the same for the triarylphosphines, except thst the constants K.sub.1, K.sub.2, K.sub.3 and K.sub.4 may be different. Those skilled in the art can determine the specific constants for other triarylphosphines with a minimum amount of experimentation as explained more fully in said application.
It is further taught in said Ser. No. 762,336 that it is generally desirable that the maximum loss of activity of the rhodium complex catalyst should be 0.75 percent per day, and highly advantageous results are achieved where the maximum rate of loss of catalyst activity is 0.3 percent per day, both being based upon the activity of the fresh catalyst. By the term "activity" is meant, for example, the amount of product produced expressed as gram-moles/liter-hour. Of course, any other standard technique can be employed to determine the relative activity of the catalyst at any given time. It should be understood, however, that the maximum acceptable rate of loss of catalyst activity would depend on many different factors, as pointed out above. The technique disclosed in said Ser. No. 762,336 provides a mechanism for obtaining any maximum rate of loss of catalyst activity by the control and correlation of the hydroformylation reaction conditions. Stated conversely, once a maximum acceptable rate of loss of catalyst activity is determined, the invention disclosed therein provides one skilled in the art with the tools of control and correlate the reaction conditions necessary to obtain catalyst stability. Therefore, the values given above for the maximum rate of loss of catalyst activity are provided merely to teach those skilled in the art how to practice that invention.
It has also been observed that the presence of an alkyldiarylphosphine (for example, propyldiphenylphosphine or ethyldiphenylphosphine) in the rhodium-catalyzed hydroformylation of the alpha-olefin propylene inhibits catalyst productivity; i.e., the rate at which the desired product aldehydes are formed. Specifically, the addition of small amounts of propyldiphenylphosphine or ethyldiphenylphosphine to rhodium hydroformylation solutions markedly reduced the rate of production of butyraldehydes from propylene, compared to the rate obtained in the absence of the alkyldiarylphosphines. This is shown by the data in Table A below:
TABLE A __________________________________________________________________________ PDPP.sup.(2) or Aldehyde TPP.sup.(1) EDPP.sup.(3) PDPP or Production Rate Compara- Amount Amount EDPP/ (gram-moles/ tive Rate (weight % (weight % TPP liter-hour) of Produc- Entry of solution) of solution) Ratio Observed Predicted.sup.(4) tion.sup.(5) __________________________________________________________________________ 1 4 PDPP (0) 0 1.03 1.02 100 2 1.89 PDPP (2.0) 1.05 0.36 1.06 34 3 3.74 PDPP (0.67) 0.18 0.53 1.02 53 4 4.06 PDPP (1.33) 0.33 0.79 1.87 42 5 3.61 PDPP (1.33) 0.37 1.51 3.51 43 6 4.0 PDPP (0.05) 0.013 0.62 1.02 60 7 9 PDPP (1.0) 0.11 0.60 0.69 87 8 6 PDPP (1.0) 0.17 0.54 0.63 86 9 9 PDPP (3.0) 0.33 0.54 0.72 75 10 6 PDPP (3.0) 0.5 0.47 0.68 68 11 9 PDPP (1.0) 0.11 0.55 0.69 80 12 6 PDPP (1.0) 0.17 0.58 0.63 92 13 9 PDPP (3.0) 0.33 0.39 0.72 54 14 6 PDPP (3.0) 0.5 0.52 0.68 77 15 9 PDPP (0) 0 0.80 0.60 greater than 100 16 0 PDPP (9) .infin. 0.273 0.60 46 17 0 PDPP (4.5) .infin. 0.213 0.47 45 18 3.89 EDPP (0.67) 0.42 1.02 42 19 3.69 EDPP (0.67) 0.42 1.02 42 20 3.88 EDPP (1.33) 0.33 1.02 33 21 6.95 EDPP (0.67) 0.32 0.82 39 22 6.85 EDPP (1.33) 0.24 0.82 29 __________________________________________________________________________ .sup.(1) TPP = triphenylphosphine .sup.(2) PDPP = propyldiphenylphosphine .sup.(3) EDPP = ethyldiphenylphosphine .sup.(4) Predicted rate determined from a kinetic rate expression ##STR3##
Although the presence of alkyldiarylphosphines in rhodium-catalyzed hydroformylation processes reduces the catalyst productivity, the stability of such rhodium complex catalysts can be enhanced by providing an alkyldiarylphosphine in the reaction medium and copending, commonly assigned U.S. application Ser. No. 762,335 filed Jan. 25, 1977 abandoned in favor of continuation U.S. application Ser. No. 140,830, now U.S. Pat. No. 4,260,828, the entire disclosure of which is incorporated herein by reference thereto, teaches that the reaction conditions can be adjusted to be more severe in order to regain this apparent loss of catalyst productivity while retaining the enhanced catalyst stability.
The invention in said Ser. No. 762,335 relates to an improvement in a rhodium-catalyzed process for hydroformylating an alpha-olefin to produce aldehydes having one more carbon atom than the alpha-olefin, which process includes the steps of reacting the alpha-olefin with hydrogen and carbon monoxide, in a liquid reaction medium which contains a soluble rhodium complex catalyst consisting essentially of rhodium complexed with carbon monoxide and a triarylphosphine ligand, wherein the improvement comprises improving the stability of the catalyst by providing in the liquid reaction medium containing the catalyst an amount of an alkyldiarylphosphine ligand; and controlling the hydroformylation reaction conditions as follows:
(1) a temperature of from about 100.degree. to about 140.degree. C.;
(2) a total gas pressure of hydrogen, carbon monoxide and alpha-olefin of less than about 450 psia;
(3) a carbon monoxide partial pressure of less than about 55 psia;
(4) a hydrogen partial pressure of less than about 200 psia;
(5) at least about 75 moles of total free phosphine ligand for each mole of catalytically-active rhodium metal present in the rhodium complex catalyst.
Said Ser. No. 762,335 further teaches that generally, the amount of the alkyldiarylphosphine ligand present in the liquid reaction medium can be from about 0.1 to about 20 percent by weight, based upon the total weight of the liquid reaction medium. When a triarylphosphine ligand is employed in the hydroformylation of an alpha-olefin, some alkyldiarylphosphine is produced in situ, the "alkyl" group thereof being derived from the alpha-olefin undergoing hydroformylation and the "aryl" groups thereof being the same as the aryl of the triarylphosphine. Therefore, it may not be necessary to add additional alkyldiarylphosphine to the reaction medium to provide a sufficient amount of the same therein. The particular amount of alkyldiarylphospine in the reaction medium will depend on several factors such as the particular alpha-olefin reacted, the reaction conditions, the desired rate of reaction, etc.
Said Ser. No, 762,335 further discloses that when an alkyldiarylphosphine ligand is present in a liquid reaction medium containing a rhodium complex catalyst consisting essentially of rhodium complexed with carbon monoxide and a triarylphosphine ligand, the resulting rhodium complex catalyst consists essentially of rhodium complexed with carbon monoxide and either one or both of the triarylphosphine ligand and the alkyldiarylphosphine ligand and that the terminology "consists essentially of" is not meant to exclude, but rather to include, hydrogen complexed with the rhodium, in addition to carbon monoxide and triarylphosphine and/or alkyldiarylphosphine. However, this language is meant to exclude other materials in amounts which poison or deactivate the catalyst.
Said Ser. No. 762,335 goes on to disclose that particularly advantageous results are achieved when the amount of total free phosphine ligand in the liquid reaction medium is at least about 100 moles per mole of catalytically-active rhodium metal present in the rhodium complex catalyst. The upper limit of the amount of total free phosphine liqand is not particularly critical and would be dictated largely by commercial and economic considerations. Higher mole ratios of total free phosphine: catalytically-active rhodium metal favor the stability of the catalyst. By "total free phosphine" is meant the triarylphosphine and/or alkyldiarylphosphine that is not tied to or complexed with the rhodium atom in the active complex catalyst. The theory of how such ligands complex with the rhodium is given in said U.S. Pat. No. 3,527, 809.
Despite the obvious advantages of the inventions discussed above the continued build-up of alkyl substituted phosphine over a period of time in a continuous hydroformylation reaction of alpha-olefins to produce aldehydes rich in the normal isomer eventually leads to an unacceptable decrease in the rate of reaction and activity of the rhodium complex catalyst due to the affinity of said alkyl substituted phosphine for the rhodium catalyst. Thus it would be clearly beneficial to the state of the art if one could selectively remove undesirable alkyl substituted phosphine from the liquid reaction medium of the hydroformylation reaction without adversely affecting the beneficial triarylphosphine and complex catalyst present therein.
However, even after enhancing the activity of the rhodium complex catalyst by removal of alkyl substituted phosphine from the hydroformylation reaction medium, eventually the rhodium complex catalyst will become spent (that is to say such enhancing procedures cannot be repeated indefinitely since eventually the activity of the catalyst will have decreased to sach a point that it is not longer economically desirable to operate the hydroformylation process) and the catalyst will have to be replaced. Moreover, improper procedures and/or contaminates, and the like at the initial start-up of a hydroformylation process could result in an early undesirabl hydroformylation medium that must also be replaced.
Upon such occurrences it becomes important to recover the rhodium values of the complex catalyst due to the inordinately high cost of rhodium. Such recovery methods will obviously entail the removal and/or destruction of the organic compounds of the hydroformylation composition, and such poses the problem of what to do with the large excess of triarylphosphine employed or the small amount of such triarylphosphine that may remain after classical removal mens, such as distillation. Accordingly, it would clearly be beneficial to the state of the art if such large or small amounts of triarylphosphine could be easily removed from such compositions or concentrates thereof, and ecologically disposed of without unduly and adversely affecting the environment.